The present invention relates generally to medical dressings and to methods of making the same, and more specifically to foam medical dressings having hydrocolloid absorptive agents incorporated in and formed integrally with at least one formed foam layer of the medical dressings to provide improved fluid uptake, retention and removal properties.
Hydrocolloids are well known and widely used in wound dressings. These agents are particularly suitable for wound dressings because of their strong absorptive properties and because they are biocompatible and noncytotoxic. In addition to the absorptive properties of hydrocolloids, various hydrocolloids, such as calcium alginates, have been reported to promote wound healing by stimulating the platelet activation and whole-blood coagulation.
Hydrocolloids are generally incorporated in wound dressings in the form of a fibrous-knitted layer. For example, U.S. Pat. No. 5,653,699 discloses a syproadsorbent-layered system in which a fibrous mat of hydrocolloids is positioned as an island on a film adhesive structure. U.S. Pat. Nos. 5,470,576, 5,792,090, and 5,764,524 also describe hydrocolloid dressings in which the hydrocolloid absorbent material is either impregnated after the fibrous dressing base is formed or is layered into the fibrous layer.
Nonfibrous alginate wound dressings are also known. U.S. Pat. No. 4,948,575, for example, describes a water-insoluble alginate hydrogel foam wound dressing that is formed in place in the wound cavity or on the wound surface from a reactive composition that foams as it gels. U.S. Pat. No. 4,393,080 also discloses a gel wound dressing that is formed of a water-soluble hydrogel of alkali metal alginate and glycerin.
More recently, U.S. Pat. No. 5,836,970 describes a chitosan/alginate foam for use as a wound dressing in which the foam is formed by admixing chitosan and alginate with a minimal amount of a solvent and then freeze drying the foam product.
The present invention provides an improved medical and wound dressing wherein during formation of the medical and wound dressing, at least one hydrocolloid is added directly to an aqueous polymerization mixture to provide at least one formed foam layer in the medical and wound dressing with the hydrocolloid absorptive agent or agents, as the case may be, integrally dispersed generally uniformly throughout the at least one formed foam layer of the wound dressing. Other ingredients may also be added to provide additional advantages to the improved medical or wound dressing.
Accordingly, it is an aspect of the present invention to provide a foam medical dressing that has improved fluid uptake and retention properties. The medical dressing includes a monolithic, polyurethane foam layer with hydrocolloid absorptive agents incorporated and formed integrally therewith. The foam layer comprises the integrated reaction products of an aqueous mixture of at least one hydrocolloid absorptive agent and hydrophilic polyurethane prepolymer. In accordance with the present invention, a prepolymer is defined as any monomeric, oligomeric or polymeric material or resin capable of undergoing further polymerization and curing into a polymeric matrix.
The incorporation of the hydrocolloid absorptive agents into the aqueous mixture for the hydrophilic polyurethane prepolymer prior to foam formation imparts certain improved and distinct properties to the formed medical dressing. Most notably, the incorporation of the hydrocolloid absorptive agents prior to foam formation xe2x80x9clocks inxe2x80x9d a substantial portion of the hydrocolloid material, thereby improving the absorption capacity of the formed foam without the need for an additional absorptive layer or post foam formation processing. The addition of the hydrocolloid absorptive agents prior to foam formation also imparts uniform exudate absorption properties and substantially reduces swelling of the formed foam upon liquid uptake which prevents the foam from losing its mechanical integrity when it becomes wet. In addition to the improved absorption properties, the incorporation of hydrocolloids prior to foam formation also imparts a slippery surface on the foam, which prevents adherence of the medical dressing to the wound bed.